Ambient temperature measurement

ABSTRACT

A temperature measuring device includes a heat plate exposed to the ambient, one or more sensor chips, and one or more device electronics that include a power transmitter, a wireless communication receiving block, and a processor. Each sensor chip includes a wireless communication transmitting block, a temperature sensor, a signal processing block, and an energy harvesting circuit. The heat plate and the sensor chips are positioned within an indent formed in an exposed surface of a device cover, such as a glass cover. The energy harvesting circuit harvests energy from an electromagnetic signal transmitted by the power transmitter. Temperature data sensed by each temperature sensor is wirelessly transmitted by the wireless communication transmitting block to the wireless communication receiving block. The processor determines an ambient temperature corrected for heat influences on the temperature sensors by internal device electronics. The temperature measuring device is implemented within a mobile electronics device.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation under 35 U.S.C. §120 of U.S.patent application Ser. No. 13/451,415, filed Apr. 19, 2012, entitled“AMBIENT TEMPERATURE MEASUREMENT,” which is hereby incorporated byreference in its entirety.

FIELD OF THE INVENTION

The present invention relates to the field of temperature measurement.More particularly, the present invention relates to the field of ambienttemperature measurement using a temperature sensor within an electronicdevice.

BACKGROUND OF THE INVENTION

Temperature sensors are commonly used to measure the ambienttemperature. However, implementing a temperature sensor within anelectronic device for the purpose of measuring ambient temperature poseschallenges. Electronic devices generate heat which affects themeasurements made by the temperature sensor. If the objective is tomeasure the ambient temperature, such as the room temperature, and notthe temperature of the electronic device within which the temperaturesensor is mounted, then the temperature sensor either must be isolatedfrom the heat generating portion of the electronic device, or the sensedtemperature must be adjusted to account for that portion attributable tothe heat generation of the electronic device. Adjusting the sensedtemperature measurements to compensate for the internal heat generationis difficult as the amount of heat generated within the electronicdevice varies based on current power being consumed, such as the amountof processing power being used, and other operational aspects of thedevice. Orientation of the device, such as standing up or laying down,and the relative position of the temperature sensor may also influencethe temperature readings since heat rises.

The location of the temperature sensor on or within the electronicdevice influences the measured temperature results. If the temperaturesensor is positioned within the housing of the electronic device, thenthe temperature sensor is exposed to the heat generating components ofthe electronic device, thereby influencing the sensed temperaturemeasurements. Further, there is little airflow into the housing formeasuring of the ambient air temperature outside the housing. As such,positioning the temperature sensor within the electronic device housingfor the purpose of measuring ambient temperature is not effective.

The temperature sensor can alternatively be positioned on an outersurface of the electronic device. However, typical housings are made ofheat conducting material, such as metal, and therefore conduct heatgenerated from within the electronic device, again influencing thesensed temperature measurements. Also, many users of handheld electronicdevices, such as cellular telephones, use protective cases over thedevice to protect from damage. Such cases block a temperature sensorpositioned on the external housing. Some electronics devices have asurface made of a non-conductive material, such as a display surface ofa cellular telephone having an exposed glass layer. When the temperaturesensor is placed on the external side of the non-conducting glass layer,the glass layer insulates the temperature sensor from the heatgenerating components internal to the device. This insulation reducesthe affects of the heat generating components on the sensed temperaturemeasurements.

Positioning the temperature sensor on the external side of the glasslayer provides insulation from the heat generating components within theelectronic device. However, simply placing the temperature sensor on theexposed surface of the glass layer is not amenable for protecting thesensor as the sensor protrudes from the surface, exposing the sensor topotentially damaging contact. Additionally, temperature sensors aretypically wired to electronic components to receive power and totransmit the measured sensed temperatures. The temperature sensor iswired to the electronic components used to operate the electronicdevice, which are also the heat generating components. The wiredconnection is heat conducting, and as such heat is conducted from theheat generating components to the temperature sensor via the wiredconnection. Providing a wired connection through the glass cover alsoposes manufacturing difficulties.

Accordingly, how can the temperature sensor distinguish between the heatgenerated by the electronic device and the ambient temperature? Further,in order to measure the ambient temperature, the temperature sensorneeds to be exposed to the ambient air. How can the temperature sensorbe assembled into the electronic device such that the temperature sensoris sufficiently exposed to the ambient air? Still further, thetemperature sensor must be insensitive to errors due to deviceorientation, humidity, pressure, and other environmental and devicerelated factors that may impact the temperature sensor measurement.

SUMMARY OF THE INVENTION

Embodiments of a temperature measuring device include a heat plateexposed to the ambient, one or more sensor chips, and one or moreinternal device electronics that include a power transmitter, a wirelesscommunication receiving block, and a processor. In some embodiments, thetemperature measuring device is implemented within a mobile electronicsdevice, such as a cellular telephone. In some embodiments, the heatplate is a metal layer or other highly thermally conductive material.The heat plate is a good heat conductor and also protects an underlyingsensor chip from mechanical damage. Each sensor chip includes a wirelesscommunication transmitting block, a temperature sensor, a signalprocessing block, and an energy harvesting circuit. In some embodiments,the heat plate and the one or more sensor chips are positioned within anindent formed in an exposed surface of a thermally insulted devicecover, such as a glass cover or other thermally insulated housing. Insome embodiments, the heat plate and the one or more sensor chips can bepositioned within a user button, such as the power button. In someembodiments, the temperature sensor assembly can be embedded in aprotective cover or carrying case of the device. Accordingly, use of theterm “cover” generally refers to surfaces that are exposed to theambient. The energy harvesting circuit within each sensor chip harvestsenergy from an electromagnetic signal transmitted by the powertransmitter. In some embodiments, the power transmitter is a circuitspecifically designed for transmitting energy to be harvested. In otherembodiments, the power transmitter also serves as the devicecommunications transmitter, such as a cellular telephone transmitterthat may periodically transmit to a base station. Temperature datasensed by each temperature sensor is wirelessly transmitted by thewireless communication transmitting block to the wireless communicationreceiving block. In this manner, the sensor chips are not wired to theinternal device electronics. The processor is configured to process thetemperature data received from each of the sensor chips. In someembodiments, the processor determines an ambient temperature correctedfor heat influences on the temperature sensors by internal deviceelectronics.

In an aspect, an electronics device is disclosed that has a devicehousing and one or more heat generating device electronics positionedwithin the device housing. The electronics device includes a heat plate,a first sensor chip, and a second sensor chip. The device electronicsinclude a power transmitter, a wireless communication receiving block,and a processor. The heat plate is exposed to the ambient. The powertransmitter is configured to transmit an electromagnetic signal. Thefirst sensor chip includes a first temperature sensor thermally coupledto the heat plate and configured to measure first temperature data, afirst energy harvesting circuit configured to harvest energy from thetransmitted electromagnetic signal, and a first wireless communicationtransmitting block configured to transmit the first temperature data.The second sensor chip includes a second temperature sensor configuredto measure second temperature data, a second energy harvesting circuitconfigured to harvest energy from the transmitted electromagneticsignal, and a second wireless communication block configured to transmitthe second temperature data. The wireless communication receiving blockis configured to receive the transmitted first temperature data and thetransmitted second temperature data. The processor is coupled to thewireless communication receiving block and configured to calculate anambient temperature according to the first temperature data and thesecond temperature data.

In some embodiments, the first sensor chip is stacked on top of thesecond sensor chip. In some embodiments, the processor is configured toperform an algorithm to calculate the ambient temperature, wherein theambient temperature is a function of the first temperature data, thesecond temperature data, a first thermal resistance between the heatplate and the first temperature sensor, and a second thermal resistancebetween the first temperature sensor and the second temperature sensor.In some embodiments, the electronic device also includes one or more ofa pressure sensor, a humidity sensor, and a gyroscope, and the firstthermal resistance is a function of data measured by one or more of thepressure sensor, the humidity sensor, and the gyroscope. In someembodiments, the second thermal resistance is a function of datameasured by one or more of the pressure sensor, the humidity sensor, andthe gyroscope. In some embodiments, the first thermal resistance, thesecond thermal resistance, or both are a function of a current powerexpenditure of the electronic device.

In some embodiments, the electronic device also includes a cover coupledto the device housing, wherein the cover is made of an insulatingmaterial and is positioned to separate the device electronics from theambient environment. In some embodiments, the cover includes an indentformed in an exposed surface of the cover, wherein the heat plate, thefirst sensor chip, and the second sensor chip are positioned within theindent. In some embodiments, the heat plate includes a first surfaceexposed to the ambient and a second surface opposite the first surfaceand facing the first sensor chip, wherein the first surface of the heatplate is co-planar with the exposed surface of the cover. In someembodiments, the insulating material comprises glass.

In some embodiments, the electronic device also includes a thermalinterface material coupled between the heat plate and the firsttemperature sensor of the first sensor chip. In some embodiments, thefirst sensor chip also includes a first signal processing circuit andthe second sensor chip also includes a second signal processing circuit.In some embodiments, the heat plate, the first sensor chip, and thesecond sensor chip are integrated within an insulating material to forma packaged temperature sensor assembly. In some embodiments, a size andshape of the packaged temperature sensor assembly is configured to matcha size and shape of the indent. In some embodiments, the electronicdevice is a mobile electronic device. In some embodiments, the secondtemperature sensor is positioned further from the heat plate and closerto the power transmitter, the wireless communication receiving block,and the processor than the first temperature sensor. In someembodiments, the first wireless communication transmitting block and thesecond wireless communication transmitting block are configured totransmit the first temperature data at a different frequency than thesecond temperature data.

In another aspect, another electronics device is disclosed that has adevice housing and one or more heat generating device electronicspositioned within the device housing. The electronics device includes aheat plate, an integrated circuit, an energy harvesting circuit, and awireless communication transmitting block. The device electronicsinclude a power transmitter, a wireless communication receiving block,and a processor. The heat plate is exposed to the ambient. The powertransmitter is configured to transmit an electromagnetic signal. Theintegrated circuit is thermally coupled to the heat plate. Theintegrated circuit has a first P-N junction for providing firsttemperature data and a second P-N junction for providing secondtemperature data. The first P-N junction is positioned at a differentdepth within the integrated circuit than the second P-N junction. Theenergy harvesting circuit is configured to harvest energy from thetransmitted electromagnetic signal, wherein the integrated circuit iscoupled to the energy harvesting circuit. The wireless communicationtransmitting block is coupled to the energy harvesting circuit and tothe integrated circuit, wherein the wireless communication transmittingblock is configured to transmit the first temperature data and thesecond temperature data. The wireless communication receiving block isconfigured to receive the transmitted first temperature data and thetransmitted second temperature data. The processor is coupled to thewireless communication receiving block and configured to calculate anambient temperature according to the first temperature data and thesecond temperature data.

In yet another aspect, another electronics device is disclosed having adevice housing and one or more heat generating device electronicspositioned within the device housing. The electronics device includes aheat plate and a sensor chip. The device electronics include a powertransmitter, a wireless communication receiving block, and a processor.The heat plate is exposed to the ambient. The power transmitter isconfigured to transmit an electromagnetic signal. The sensor chipincludes a temperature sensor thermally coupled to the heat plate andconfigured to measure temperature data, an energy harvesting circuitconfigured to harvest energy from the transmitted electromagneticsignal, and a wireless communication transmitting block configured totransmit the first temperature data. The wireless communicationreceiving block is configured to receive the transmitted temperaturedata. The processor is coupled to the wireless communication receivingblock and is configured to calculate an ambient temperature according tothe temperature data.

BRIEF DESCRIPTION OF THE DRAWINGS

Several example embodiments are described with reference to thedrawings, wherein like components are provided with like referencenumerals. The example embodiments are intended to illustrate, but not tolimit, the invention. The drawings include the following figures:

FIG. 1 illustrates a cut-out side view of a portion of a device housinghaving an indent formed in an exposed surface according to anembodiment.

FIG. 2 illustrates the configuration of FIG. 1 including a temperaturesensor assembly positioned in the indent.

FIGS. 3-7 illustrate various exemplary configurations of the temperaturesensor assembly according to some embodiments.

FIG. 8 illustrates a cut-out side view of a portion of an electronicdevice according to an embodiment.

FIG. 9 illustrates a conceptual block diagram of the relevant componentsof the device electronics for implementing the temperature measuringdevice.

FIG. 10 illustrates a conceptual block diagram of the relevantcomponents within the sensor chip for implementing the temperaturemeasuring device.

FIG. 11 illustrates a cut-out side view of a temperature sensor assemblyhaving two sensor chips according to an embodiment.

FIG. 12 illustrates a simplified conceptual model of the thermal pathbetween the ambient and the internal heat sources according to anembodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present application are directed to a temperaturemeasuring device. Those of ordinary skill in the art will realize thatthe following detailed description of the temperature measuring deviceis illustrative only and is not intended to be in any way limiting.Other embodiments of the temperature measuring device will readilysuggest themselves to such skilled persons having the benefit of thisdisclosure.

Reference will now be made in detail to implementations of thetemperature measuring device as illustrated in the accompanyingdrawings. The same reference indicators will be used throughout thedrawings and the following detailed description to refer to the same orlike parts. In the interest of clarity, not all of the routine featuresof the implementations described herein are shown and described. Itwill, of course, be appreciated that in the development of any suchactual implementation, numerous implementation-specific decisions mustbe made in order to achieve the developer's specific goals, such ascompliance with application and business related constraints, and thatthese specific goals will vary from one implementation to another andfrom one developer to another. Moreover, it will be appreciated thatsuch a development effort might be complex and time-consuming, but wouldnevertheless be a routine undertaking of engineering for those ofordinary skill in the art having the benefit of this disclosure.

FIG. 1 illustrates a cut-out side view of a portion of a device housinghaving an indent formed in an exposed surface according to anembodiment. In some embodiments, the device housing is for a mobileelectronics device, such as a cellular telephone. In some embodiments,the portion of the device housing having the indent is a top cover ofthe device. The portion of the device housing having an indent isdescribed hereafter as being a glass cover, which is commonly used asthe top cover of a cellular telephone or other mobile electronicdevices. In general, the portion of the device housing having the indentis non-metallic, having good thermal insulation characteristics. It isunderstood that the portion of the device housing with indent is notrestricted to the top cover of the device housing, but can alternativelybe configured as a side or bottom portion of the device housing. Asshown in FIG. 1, an indent 6 is formed in an external surface 4 of a topglass cover 2. The surface 4 is exposed to the ambient environment. Theindent 6 is configured to receive a temperature sensor assembly 9, asshown in FIG. 2. The temperature sensor assembly 9 includes a sensorchip 10 having a temperature sensor 12, and a heat plate, such as ametal layer 14. The metal layer 14 is thermally coupled to the sensorchip 10 using a thermal interface material, such as solder balls 8. Itis understood that alternative thermal interface materials can be used.The temperature sensor assembly 9 is secured in the indent 6, such asusing an adhesive. The metal layer 14 covers the temperature sensor 12so that the temperature sensor 12 is protected from direct exposure tothe environment. In some embodiments, the exposed surface of the metallayer 14 is co-planar with the exposed surface 4. Once the temperaturesensor assembly 9 is positioned within the indent 6, a polishing stepcan be performed to achieve this result.

The temperature sensor assembly 9 can be assembled as an integratedpackage. FIGS. 3-7 illustrate various exemplary configurations of thetemperature sensor assembly according to some embodiments. FIG. 3 showsa metal layer 24 extending beyond the footprint of a sensor chip 20 anda temperature sensor 22. The metal layer 24 and the sensor chip 20 canbe packaged within an insulating material 26. The indent and packagedtemperature sensor assembly are configured such that the packagedtemperature sensor assembly fits within the indent. In some embodiments,the indent is formed solely for the purpose of receiving the temperaturesensor assembly. In other embodiments, the indent used to receive thetemperature sensor assembly is part of a larger indent formed foranother purpose. For example, logos on a cellular telephone can be“printed” or etched into the device cover. The temperature sensorassembly can be placed under a logo block or made as part of the logoblock. The shape of the metal layer 24 and the packaged temperaturesensor assembly can be application specific. FIG. 5 illustrates a topdown view of an exemplary circular configuration of the metal layer 24and the insulating material 26. The corresponding indent is alsocircular to accommodate the shape of the packaged temperature sensorassembly. FIG. 6 illustrates a top down view of an exemplary squareconfiguration of the metal layer 24′ and the insulating material 26′.The corresponding indent is also square to accommodate the shape of thepackaged temperature sensor assembly. FIGS. 3, 5, and 6 show theinsulating material as extending beyond the footprint of the metallayer. FIG. 4 illustrates an alternative configuration in which aninsulating material 36 is configured within the footprint of the metallayer 24. FIG. 7 illustrates a bottom up view of an exemplarysquare-shaped metal layer 24′ and insulating material 36 according tothe configuration of FIG. 6. It is understood that the metal layer, thetemperature sensor assembly, the packaged temperature sensor assembly,and the indent can be shaped and sized differently than thoseconfigurations shown in FIGS. 2-7.

FIG. 8 illustrates a cut-out side view of a portion of an electronicdevice according to an embodiment. In an exemplary application, theelectronic device is a cellular telephone.

Although the electronic device is subsequently described in terms of acellular telephone, it is understood that the temperature measuringconcepts can also be applied to other types of electronics devices. Thecellular telephone includes the temperature sensor assembly 9 and theglass cover 2 with indent 6 of FIG. 2 and also a printed circuit board(PCB) 40 having device electronics 42, 44, 46. The device electronics42, 44, 46 are representative of any heat sources within the cellulartelephone, either on or off the PCB 40. Examples of device electronicsinclude, but are not limited to, a central processing unit (CPU) orother processing component, memory, and power supply. The deviceelectronics are also representative of any heat externally added to thedevice through thermally conductive portions of the housing, for examplethe body heat of a user holding the device.

The temperature measuring device uses energy harvesting to provide powerto the sensor chip and wireless communications to communicate databetween the sensor chip and the internal device electronics. In thismanner, wires are not used to provide power to the sensor chip, nor arewires used to communicate measured temperature data from the sensor chipto the internal device electronics. This wireless application eliminatesmanufacturing complexities associated with hard wiring the temperaturesensor assembly to the internal device electronics through the glasscover. This wireless application also eliminates heat transfer to thetemperature sensor that may occur due to a wired connection to a heatgenerating device. FIG. 9 illustrates a conceptual block diagram of therelevant components of the device electronics for implementing thetemperature measuring device according to an embodiment. The relevantcomponents include a power transmitter 48 and an RF communication block50. In an exemplary application, the power transmitter 48 and the RFcommunication block 50 are included within the device electronic 44,which also includes a central processing unit. In some embodiments, thepower transmitter 48 and the RF communication block 50 are integrated aspart of a single chip, such as shown in FIG. 9. In other embodiments,the power transmitter 48 and the RF communication block 50 are discretecomponents, or are included in separate chips. FIG. 10 illustrates aconceptual block diagram of the relevant components within the sensorchip 10 for implementing the temperature measuring device according toan embodiment. The sensor chip 10 includes the temperature sensor 12, anRF communication block 52, an energy harvesting circuit 54, and a signalprocessing block 56.

In operation, the power transmitter 48 transmits a wirelesselectromagnetic signal, such as an RF signal, that is received by theenergy harvesting circuit 54 and harvested for energy. Harvesting energyin this manner is well known in the art and any conventional energyharvesting circuit can be used to implement the energy harvestingcircuit 54. The harvested energy is used to power the sensor chip 10. Insome embodiments, the power transmitter 48 is positioned directlyunderneath, or approximately underneath, the sensor chip 10. Since thedistance between the power transmitter 48 and the energy harvestingcircuit 54 is small, the generated electromagnetic signal can below-powered. In some embodiments, the sensor chip 10 is configured forlow-power consumption, such as in the microwatt range, thereby furtherreducing the power requirements for the electromagnetic signaltransmitted by the power transmitter 48. The power transmitter 48 isunder processor control, either from a on-chip processing element or aseparate component electrically coupled to the device electronic 44, andthe electromagnetic signal is transmitted by the power transmitter 48when a temperature measurement is required. The transmission periodicitycan be adjusted according to the desired need for a temperaturemeasurement, current power levels of the device, or some other criteria.In most applications, a temperature measurement is only neededperiodically, and therefore the sensor chip does not have to becontinuously powered. In this sense, the power transmitter 48 generatesbursts of power, programmed to a desired burst frequency. Decreasing theburst frequency conserves power. In an exemplary application, as thedevice battery level decreases, the burst frequency can becorrespondingly decreased.

Upon energy harvesting the electromagnetic signal received by the energyharvesting circuit 54, the sensor chip 10 powers on for a shortduration. While powered on, a temperature measurement is made by thetemperature sensor 12 and the signal processor block 56. The temperaturemeasurement is then transmitted as temperature data by the RFcommunication block 52. The data transmitted can represent thetemperature measurement in any of a variety of ways including, but notlimited to, a binary stream, a pulse-width modulated signal whose dutycycle represents the temperature measurement, and a series of pulseswhose timing interval is representative of the temperature measurement.As used herein, the “temperature data” is used generically to indicatedata representative of the temperature measurement. The transmittedtemperature data is received by the RF communication block 50 andprocessed accordingly, such as by the CPU included within the deviceelectronic 44.

Since glass is a thermal insulator, the glass cover 2 provides thetemperature sensor 12 a degree of thermal insulation from the heatgenerated within the cellular telephone by the device electronics 42,44, 46. In an ideal application, the cover having the indent would havean infinite thermal resistance, thereby completely isolating thetemperature sensor 12 from any heat generated within the cellulartelephone. In such an ideal case, a single temperature sensor issufficient to measure the ambient temperature, as the temperaturemeasured by the single temperature sensor would not be effected by anyinternally generated heat. Even in this ideal case, there is some amountof non-ambient heat due to harvesting the electromagnetic signal andoperating the sensor chip. Configuring the sensor chip as a low-powercircuit significantly minimizes this effect on the temperaturemeasurement. Additionally, the amount of power harvested and used by thesensor chip is a known quantity, which can be accounted for andsubtracted out when the measured temperature data is processed.

In practice however, the glass cover 2 has a finite thermal resistanceand therefore heat generated from within the cellular telephone has someeffect on the temperature measured by the temperature sensor 12. In someembodiments, additional insulation can be added within the sensor chip10 and/or within the packaged temperature sensor assembly so as toprovide additional heat insulation between the temperature sensor 12 andthe heat sources within the cellular telephone.

To provide a greater accuracy of measured ambient temperature, anotherembodiment of the temperature sensor system adjusts the measuredtemperature data to compensate for external effects on the temperaturesensor. In these embodiments, the temperature sensor assembly isconfigured with at least two temperature sensors positioned so as todetermine a temperature gradient.

FIG. 11 illustrates a cut-out side view of a temperature sensor assembly60 having two sensor chips according to an embodiment. The temperaturesensor assembly 60 includes a metal layer 64, a sensor chip 70 having atemperature sensor 72, and a sensor chip 80 having a temperature sensor82. The metal layer 64 is thermally coupled to sensor chip 70 using athermal interface material, such as solder balls 68. It is understoodthat alternative thermal interface material can be used. In someembodiments, the sensor chip 70 is secured to the sensor chip 80, suchas via an adhesive 66. In some embodiments, the temperature sensorassembly 60 is secured in the indent, such as using an adhesive. It isunderstood that the temperature sensor assembly 60 can be alternativelyshaped and/or sized, or packaged to form a packaged temperature sensorassembly, in a manner similar to that described above in regards to thesingle temperature sensor configurations. The metal layer 64 covers thetemperature sensor 72 so that the temperature sensor 72 is protectedfrom direct exposure to the environment. In some embodiments, theexposed surface of the metal layer 64 is co-planar with the exposedsurface 4 (FIG. 1). Once the temperature sensor assembly 60 ispositioned within the indent, a polishing step can be performed toachieve this result. It is understood that alternative planarizingmethods can be used.

Each of the sensor chips 70 and 80 function similarly as the sensor chip10 described above in relation to the temperature measuring device ofFIG. 8. In the case of the temperature sensor assembly 60, two sets ofmeasured temperature data are measured and transmitted to the deviceelectronics for processing. Each sensor chip 70 and 80 preferablytransmits at a different frequency to avoid interference. It isunderstood that alternative communication mechanisms can be used. Forexample, the second sensor chip listens for the first sensor tocommunicate, then the second sensor starts its communication.

As described above, the measurement obtained by temperature sensor 72 isinfluenced by both the ambient temperature and the heat generated by theheat sources within the cellular telephone. A thermal path between theambient and the internal heat sources can be modeled and used to applyone or more correction factors for determining a more accurate ambienttemperature measurement. FIG. 12 illustrates a simplified conceptualmodel of the thermal path between the ambient and the internal heatsources according to an embodiment. Thermal resistance and electricalresistance are quite analogous to each other. As such, each thermalresistance in the thermal path can be modeled as an equivalentelectrical resistance. The thermal resistance between the temperaturesensor 72 and the ambient is represented as resistor R1. The thermalresistance between the temperature sensor 82 and the temperature sensor72 is represented as resistor R2. The thermal resistance between theinternal heat sources and the temperature sensor 82 is represented asresistor R3. The ambient temperature is represented as temperature TA,the temperature measured by the temperature sensor 72 is represented astemperature T1, the temperature measured by the temperature sensor 82 isrepresented as temperature T2, and the temperature of the internal heatsources is represented as temperature T3. The thermal path isrepresentative of a resistive divider network having the followingrelationships:

-   -   If        R3>>R1+R2 or If R2>>R1,        Then        (T2−T1)/R2=(T1−TA)/R1        Solving for TA results in:        TA=−(R1/R2)*T2+((R1+R2)/R3)*T1  (1)        The values of resistors R1 and R2 can be well characterized and        are therefore considered to be known quantities. In some        embodiments, the values of resistors R1 and R2 are predetermined        and stored in memory for subsequent use. In other embodiments, a        self-test can be administered to determine the real-time values        of the resistors R1 and R2, which are then stored in memory.        Equation (1) is programmed into the processor, such as the CPU        in device electronic 44 of FIG. 9, and the ambient temperature        TA is determined using the known values of resistors R1 and R2        and the measured values for temperatures T1 and T2.

As shown in equation (1), the relationship of the thermal resistancesand the measured temperatures provides correction factors fordetermining the ambient temperature TA. In the case where resistanceR1=0, which corresponds to the ideal case where the metal layer is aperfect thermal conductor, then the ambient temperature TA is equal tothe measured temperature T1 of the temperature sensor 72 multiplied bythe ratio of the resistances R2 and R3. An assumption of equation (1) isthat heat flows outward, from the inside of the cellular telephone tothe ambient, and therefore a negative correction factor, −(R1/R2)*T2, isapplied. Under this assumption, equation (1) indicates that the ambienttemperature is less than the temperature T1 measured by the temperaturesensor 72 because there is some heat added by the internal heat sources.If the temperature T1 is greater than the temperature T2, then a reverseflow of heat is indicated, which is an error condition. Such a conditionmay occur, for example, if the metal layer is exposed to direct sunlightor other external heat source.

In some embodiments, the values of the resistors R1 and R2 can bedetermined as a function, such as a function of pressure, humidity,orientation of the device, or some other variable, or combination ofvariables. These variables can be values measured by other sensors onthe cellular telephone. For example, a cellular telephone can beconfigured with a pressure sensor for determining altitude, or agyroscope for measuring the tilt, or orientation of the device.Orientation may impact the temperature measurement due to the locationof the temperature sensor and the fact that hotter air rises. Themeasured values for these variables can be compared to the initializedvalues used when the device was originally calibrated. The difference invalues can then be used to adjust the values of the resistors R1 and R2.The values of the resistance R1 and R2 can also be adjusted according tothe current power level of the cellular telephone. In general,algorithms can be developed to compensate for errors due to variableoperating conditions. The operating conditions are initiallycharacterized during manufacturing. Look-up tables can be used toprovide correction factors according to real-time operating conditions.

Conceptually, the ambient temperature is calculated using a temperaturegradient, where the temperature gradient is determined by measuringtemperatures at different points along a vector from inside the deviceto the ambient. In the embodiments described above, two discretetemperature sensor elements are positioned at two different locationsalong the vector to measure two positional temperatures. In analternative embodiment, a monolithic configuration is used having twodifferent junctions, separately positioned along a vector from insidethe device to the ambient, where the two different junctions are eachaccessible for measuring a temperature at the junction. In an exemplaryapplication, the temperature is measured at two different junctions of avertical or horizontal P-N-P transistor. The measured temperature ateach P-N junction varies depending on the depth of the P-N junctions inthe transistor.

Embodiments of the temperature measuring device described herein aredirected to an energy harvesting system that includes a powertransmitter and an energy harvesting circuit to harvest energy from anelectromagnetic signal transmitted by the power transmitter. In otherembodiments, other energy harvesting mechanisms are considered. In anexample, a solar cell is used, such as a solar cell built into the topcover or placed adjacent to the heat plate, and the solar cell iscoupled to the one or more sensor chips. In still other embodiments, thepower transmitter is a light source, and the solar cell harvests energyfrom the light emitted by the light source. In this case, the solar cellis coupled to the sensor chip, or is part of the sensor chip, and can bepositioned anywhere that enables exposure to the light emitted by thelight source.

Embodiments of the temperature measuring device described herein aredirected to positioning the temperature sensor assembly within thedevice top cover. In other embodiments, the temperature sensor assemblycan be embedded in a protective cover or carrying case of the device.For example, in a cellular telephone, the protective cover is aninsulating sleeve that slips on to the phone. In this way, thetemperature sensor assembly becomes an accessory. The temperature sensorassembly can store calibration data, and can transmit this calibrationdata whenever a temperature measurement is transmitted.

The present application has been described in terms of specificembodiments incorporating details to facilitate the understanding of theprinciples of construction and operation of the temperature measuringdevice. Many of the components shown and described in the variousfigures can be interchanged to achieve the results necessary, and thisdescription should be read to encompass such interchange as well. Assuch, references herein to specific embodiments and details thereof arenot intended to limit the scope of the claims appended hereto. It willbe apparent to those skilled in the art that modifications can be madeto the embodiments chosen for illustration without departing from thespirit and scope of the application.

What is claimed is:
 1. An electronics device having a device housing andone or more heat generating device electronics positioned within thedevice housing, the electronics device comprising: the deviceelectronics comprising a power transmitter configured to transmit anelectromagnetic signal; a first sensor chip comprising a firsttemperature sensor thermally coupled to a heat plate exposed to anambient environment, the first sensor chip configured to measure firsttemperature data, a first energy harvesting circuit configured toharvest energy from the transmitted electromagnetic signal, and a firstwireless communication transmitting block configured to transmit thefirst temperature data; a second sensor chip comprising a secondtemperature sensor configured to measure second temperature data, asecond energy harvesting circuit configured to harvest energy from thetransmitted electromagnetic signal, and a second wireless communicationblock configured to transmit the second temperature data; the deviceelectronics comprising a wireless communication receiving blockconfigured to receive the transmitted first temperature data and thetransmitted second temperature data; and the device electronicscomprising a processor coupled to the wireless communication receivingblock and configured to calculate an ambient temperature according tothe first temperature data and the second temperature data.
 2. Theelectronic device of claim 1 wherein the first sensor chip is stacked ontop of the second sensor chip.
 3. The electronic device of claim 1wherein the processor is configured to perform an algorithm to calculatethe ambient temperature, wherein the ambient temperature is a functionof the first temperature data, the second temperature data, a firstthermal resistance between the heat plate and the first temperaturesensor, and a second thermal resistance between the first temperaturesensor and the second temperature sensor.
 4. The electronic device ofclaim 3 wherein the electronic device further comprises one or more of apressure sensor, a humidity sensor, and a gyroscope, and the firstthermal resistance is a function of data measured by one or more of thepressure sensor, the humidity sensor, and the gyroscope.
 5. Theelectronic device of claim 3 wherein the electronic device furthercomprises one or more of a pressure sensor, a humidity sensor, and agyroscope, and the second thermal resistance is a function of datameasured by one or more of the pressure sensor, the humidity sensor, andthe gyroscope.
 6. The electronic device of claim 3 wherein the firstthermal resistance is a function of a current power expenditure of theelectronic device.
 7. The electronic device of claim 3 wherein thesecond thermal resistance is a function of a current power expenditureof the electronic device.
 8. The electronic device of claim 1 whereinthe heat plate, the first sensor chip, and the second sensor chip areintegrated within an insulating material to form a packaged temperaturesensor assembly.
 9. The electronic device of claim 1 further comprisinga cover coupled to the device housing, wherein the cover comprises aninsulating material and is positioned to separate the device electronicsfrom the ambient environment.
 10. The electronic device of claim 9wherein the cover includes an indent formed in an exposed surface of thecover, wherein the heat plate, the first sensor chip, and the secondsensor chip are positioned within the indent.
 11. The electronic deviceor claim 10 wherein the heat plate includes a first surface exposed tothe ambient and a second surface opposite the first surface and facingthe first sensor chip, wherein the first surface of the heat plate isco-planar with the exposed surface of the cover.
 12. The electronicdevice of claim 10 wherein the heat plate, the first sensor chip, andthe second sensor chip are integrated within an insulating material toform a packaged temperature sensor assembly, further wherein a size andshape of the packaged temperature sensor assembly is configured to matcha size and shape of the indent.
 13. The electronic device of claim 9wherein the insulating material comprises glass.
 14. The electronicdevice of claim 1 further comprising a thermal interface materialcoupled between the heat plate and the first temperature sensor of thefirst sensor chip.
 15. The electronic device of claim 1 wherein thefirst sensor chip further comprises a first signal processing circuitand the second sensor chip further comprises a second signal processingcircuit.
 16. The electronic device of claim 1 wherein the electronicdevice comprises a mobile electronic device.
 17. The electronic deviceof claim 1 wherein the second temperature sensor is positioned furtherfrom the heat plate and closer to the power transmitter, the wirelesscommunication receiving block, and the processor than the firsttemperature sensor.
 18. The electronic device of claim 1 wherein thefirst wireless communication transmitting block and the second wirelesscommunication transmitting block arc configured to transmit the firsttemperature data at a different frequency than the second temperaturedata.
 19. An electronics device having a device housing and one or moreheat generating device electronics positioned within the device housing,the electronics device comprising: the device electronics comprise apower transmitter configured to transmit an electromagnetic signal; anintegrated circuit thermally coupled to a heat plate exposed to anambient environment, the integrated circuit having a first P-N junctionfor providing first temperature data and a second P-N junction forproviding second temperature data, wherein the first P-N junction ispositioned at a different depth within the integrated circuit than thesecond P-N junction, an energy harvesting circuit configured to harvestenergy from the transmitted electromagnetic signal, wherein theintegrated circuit is coupled to the energy harvesting circuit; awireless communication transmitting block coupled to the energyharvesting circuit and to the integrated circuit, wherein the wirelesscommunication transmitting block is configured to transmit the firsttemperature data and the second temperature data; the device electronicscomprising a wireless communication receiving block configured toreceive the transmitted first temperature data and the transmittedsecond temperature data; and the device electronics comprising aprocessor coupled to the wireless communication receiving block andconfigured to calculate an ambient temperature according to the firsttemperature data and the second temperature data.
 20. An electronicsdevice having a device housing and one or more heat generating deviceelectronics positioned within the device housing, the electronics devicecomprising: the device electronics comprise a power transmitter configured to transmit an electromagnetic signal; a sensor chip comprisinga temperature sensor thermally coupled to a heat plate exposed to anambient environment, the sensor chip configured to measure temperaturedata, an energy harvesting circuit configured to harvest energy from thetransmitted electromagnetic signal, and a wireless communicationtransmitting block configured to transmit the first temperature data;the device electronics comprising a wireless communication receivingblock configured to receive the transmitted temperature data; and thedevice electronics comprising a processor coupled to the wirelesscommunication receiving block and configured to calculate an ambienttemperature according to the temperature data.